This invention relates generally to high frequency microwave frequency amplifiers and more particularly to a stripline microwave traveling wave device and method.
There exists a great need for amplifiers at microwave signals particularly millimeter and submillimeter wave frequencies for communications, radar, scientific studies and other applications. Some needs are for small signal amplifiers such as in receivers where not very much output power is needed. There are needs for higher power amplifiers such as those used for transmitters, sources, etc. While there is currently a great variety of amplifiers there is a constant need to make them smaller, lighter, more powerful, more efficient, lower voltage, higher gain, wider bandwidth, lower noise, more rugged, longer-lifed, lower cost, etc.
Current traveling-wave tubes generate high voltage electron beams (usually several kilovolts to many tens of kilovolts) which travel adjacent periodic slow-wave circuits which carry the signals with the signal electric fields coupled to the electron beam whereby energy is transferred from the beam to the traveling signal wave. Slow wave circuits are usually helix or coupled-cavity circuits. An axial magnetic field is normally required to focus and confine the electron beams. The high voltage and magnetic field required contribute substantially to size and weight of the tube. As the frequency of operation is increased the requirement of high voltage and magnetic field strength increases. As the frequency is increased the slow-wave circuit becomes smaller and at even low millimeter wave frequencies the circuits become difficult and expensive to manufacture. For that reason there are very few practical amplifiers which operate above about 100 GHz. Oscillators are generally used because oscillators are generally simpler in construction and less expensive to manufacture.
The present invention makes use of an entirely different principle in which electrons are emitted from a cathode stripline accelerated by a DC voltage, and simultaneously modulated by the electric field of the microwave signal traveling along a gate stripline. The electrons give up their energy to the RF electric field which has reversed in direction at the gate stripline. A positive feedback from the growing wave to the modulating signal contributes to the amplifier having a large and continuous exponential gain. This traveling wave amplifier requires no magnetic field or periodic slow-wave structure and operates at low voltage. In addition, it is very small and can be constructed using solid state type integration techniques.
By simply taking a small piece or section of a traveling-wave amplifier with appropriate connections such as high-reflection terminations at the ends to create a standing wave, or simply using a piece or section in a cavity, oscillators can be constructed.